The wave/particle duality of electrons is an important aspect of quantum mechanical descriptions of their behavior. Most simple descriptions of electrons refer only to their particle nature, with discussions of the wave nature reserved for considerations of physical features on the order of a few tens of nanometers.
The Schrodinger equation describes the motion of an electron as the evolution of a wave extended in space. Some examples of phenomena which depend upon the wave nature of electrons are the Ramsauer-Townsend effect, Fresnel diffraction from a sharp boundary and diffraction from an electrostatic double prism. See H. Haken and H. C. Wolf, Atomic and Quantum Physics, (Springer-Verlag, New York, 1984). Diffraction of electrons has been applied in such analytical techniques as Low Energy Electron Diffraction Spectroscopy (LEEDS) and Reflection High Energy Electron Diffraction (RHEED). See M. G. Lagally, "Low Energy Electron Diffraction," in Metals Handbook ninth edition. vol. 10, 536, edited by R. E. Whan, American Society for Metals, Metals Park, Ohio (1986).
All of the effects noted above were observed in vacuum. Most solid state electron devices exhibit essentially particle-like behavior, with their wave nature entering the analysis only through a band structure computation. Direct observation of electron wave phenomena is possible only in devices having feature sizes comparable to characteristic electron wavelengths. Such devices have been developed using new epitaxial growth and lithographic techniques. Prominent examples are the Resonant Tunneling diode, R. Tsu and L. Esaki, "Tunneling in a finite superlattice", Appl. Phys. Lett. 22. 562 (1973); and small rings for observing the Aharonov-Bohm effect. S. Datta et al., Phys. Rev. Lett., 55 (21), 2344 (1985). In these devices, current oscillations arise from constructive and destructive interference of electron waves. The Aharonov-Bohm experiments demonstrate that effects can be observed which require phase coherence on the scale of a micron.
Some solid state devices exist which exhibit electron interference, but none exhibit diffraction. The QUADFET of this invention will enable Fraunhofer diffraction to be demonstrated and exploited. These devices are High Electron Mobility Transistors (HEMTs), in which the source and a specially-formed drain perform the functions of the light source and "viewing screen" of an analogous optical system, respectively. A device has been proposed which utilizes electron diffraction, but whose construction differs markedly from that of the device of the present invention. See K. Furuya, J. Appl. Phys. 62 (4), 15 Aug. 1987.